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5635d99953
The TIF_SPEC_IB bit does not need to be evaluated in the decision to invoke __switch_to_xtra() when: - CONFIG_SMP is disabled - The conditional STIPB mode is disabled The TIF_SPEC_IB bit still controls IBPB in both cases so the TIF work mask checks might invoke __switch_to_xtra() for nothing if TIF_SPEC_IB is the only set bit in the work masks. Optimize it out by masking the bit at compile time for CONFIG_SMP=n and at run time when the static key controlling the conditional STIBP mode is disabled. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Ingo Molnar <mingo@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Jiri Kosina <jkosina@suse.cz> Cc: Tom Lendacky <thomas.lendacky@amd.com> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: David Woodhouse <dwmw@amazon.co.uk> Cc: Tim Chen <tim.c.chen@linux.intel.com> Cc: Andi Kleen <ak@linux.intel.com> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Casey Schaufler <casey.schaufler@intel.com> Cc: Asit Mallick <asit.k.mallick@intel.com> Cc: Arjan van de Ven <arjan@linux.intel.com> Cc: Jon Masters <jcm@redhat.com> Cc: Waiman Long <longman9394@gmail.com> Cc: Greg KH <gregkh@linuxfoundation.org> Cc: Dave Stewart <david.c.stewart@intel.com> Cc: Kees Cook <keescook@chromium.org> Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20181125185005.374062201@linutronix.de
40 lines
1.1 KiB
C
40 lines
1.1 KiB
C
// SPDX-License-Identifier: GPL-2.0
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//
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// Code shared between 32 and 64 bit
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#include <asm/spec-ctrl.h>
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void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p);
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/*
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* This needs to be inline to optimize for the common case where no extra
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* work needs to be done.
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*/
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static inline void switch_to_extra(struct task_struct *prev,
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struct task_struct *next)
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{
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unsigned long next_tif = task_thread_info(next)->flags;
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unsigned long prev_tif = task_thread_info(prev)->flags;
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if (IS_ENABLED(CONFIG_SMP)) {
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/*
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* Avoid __switch_to_xtra() invocation when conditional
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* STIPB is disabled and the only different bit is
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* TIF_SPEC_IB. For CONFIG_SMP=n TIF_SPEC_IB is not
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* in the TIF_WORK_CTXSW masks.
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*/
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if (!static_branch_likely(&switch_to_cond_stibp)) {
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prev_tif &= ~_TIF_SPEC_IB;
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next_tif &= ~_TIF_SPEC_IB;
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}
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}
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/*
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* __switch_to_xtra() handles debug registers, i/o bitmaps,
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* speculation mitigations etc.
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*/
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if (unlikely(next_tif & _TIF_WORK_CTXSW_NEXT ||
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prev_tif & _TIF_WORK_CTXSW_PREV))
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__switch_to_xtra(prev, next);
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}
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